"Come on, just try it," Omilaena said.
Kai snorted. "You can't be serious."
"I am absolutely, 100% serious."
"We're running out of time to prepare for the incursion."
"Sure, but you need to train the flexibility of your monstrous abilities, don't you?"
When Kai had first created Monstrous Tail as an ability, he had been thinking about nothing but gaining an additional striking limb that might be useful against multiple opponents. He'd experimented a little with using it for precise operations, only thinking that he might be able to pick up noncombatants while keeping the rest of his body free to fight.
Using it for sex had never occurred to him, but he shouldn't have underestimated Omilaena.
"At least try for me." Omilaena leaned toward him and batted her eyelashes exaggeratedly. "You've already created different sorts of spikes for your tail, and there's benefit to gaining more flexibility. Can you even do a blunt head?"
"Don't think I don't see what you're doing," Kai said, even as he began to grow a physical tail.
"Enticing my husband with a challenge instead of a promise of sex? Don't think I'm unaware of the horrors of my marriage."
Despite her tone, Omilaena eagerly watched his tail as it grew to a length longer than his entire body, then ended in a blunt tip. Usually Kai made it end with a spike, but he had managed to prevent that part of the transformation. He wanted to do more than that; she had actually made a good point about dealing blunt damage being a potentially valuable skill, especially if certain types of armored monsters appeared.
So Kai closed his eyes and focused, trying to reshape the end of his tail. He focused on the metal-like material that usually formed a spike, but tried to keep it blunt. Gradually he felt the tip lengthen and harden - something he was definitely not saying aloud where Omilaena could hear - and when he opened his eyes, he saw that his tail now ended in what looked almost like a metal rod.
"Ooh, great shape to start!" Omilaena said, clapping appreciatively.
"But not a great mace." Kai gritted his teeth as he focused further, and to his surprise it was fairly easy to make spikes protrude from the rod - spikes seemed to come easily to monstrous transformations. "There, that's a viable weapon, which is all you every cared about, right?"
"Don't underestimate my kinkiness." Omilaena grabbed his tail with one hand and pulled it to her face, where she promptly licked up the side of the macehead. "Do you feel that, by the way?"
"Just like touching something with a fingernail. It's not very sensitive."
"That's a shame, because if you make those spikes a little smaller, I'll fellate this thing."
"Don't start fellating random weapons." Kai pulled his tail out of her grip, and Omilaena pouted, but a second later he thrust it between her legs, wrapping around one of her thighs. With his new control, it was easy to pull her entire body against him.
"Ooh, see! You're getting into it already!" Omilaena happily draped herself against his chest and then gave him a kiss that was more affectionate than sexual. "But really, won't you try for me? I honestly want to explore this."
"I'm working on it," Kai said, "but you're going to have to stop distracting me."
"I absolutely will not. You need control under pressure, after all."
She continued to kiss him while grinding her body against his. To fight back, Kai slid his tail further even as he moved it up, so the thicker portion of the tail parted her thighs and rubbed against her pussy. Soon he had Omilaena groaning appreciatively and she began rocking her hips against his tail. Kai's monstrous body parts might not be overly sensitive, but he could feel his wife's heat as she ground against the muscular tail and he had to admit it did something for him.
Kai brought up the end of the tail again, focusing on reshaping the tip. She wanted it to be a dick, and he wasn't sure he could make softer tissue, but he could at least create a tail-head from muscular tissue instead of armor. Soon he enough he'd managed to create an oblong... well, it was a phallus, there was no getting around that.
Instead of announcing it, Kai kept kissing Omilaena while he slid the new tip between the cheeks of her ass. He saw her eyes fly open and she pulled back, looking over her shoulder with an expression of delight. Honestly, that alone was worth the trouble.
"Now you're getting into it," she said with a grin. "But give me more of a flared tip, will you? And a fat bulge through the center, just like yours. Not to say I don't want to experiment later, but..."
After several more rounds of requests, Kai had what she apparently wanted. Omilaena wriggled against him happily, sticking out her ass enough for the tail to penetrate. He went extremely slowly at first, concerned that he was going to hurt her, but her pussy was soaking wet. When the tail slipped inside she let out an appreciative murmur.
"See? That wasn't so hard... now fuck me with it..."
That actually proved trickier than the first steps, because he needed to control the force through the tail and could easily go too deep. Soon enough, however, Kai was pumping his tail into Omilaena from behind. It didn't feel like having his own cock inside his wife, more like pushing fingers inside her, but he loved the way it made her react. The momentum of his thrusts was reversed, which meant that he was effectively fucking her against his own chest, which he had to admit was interesting.
All of this left his cock as a bar of iron, trapped between his stomach and hers. Even as he kept pumping the tail inside her, Kai caught her tossing head and made her look at him.
"Now what?" he asked. "Because it seems great for you, but this just means my cock gets ignored."
"Not for long." Omilaena lifted her hips off the tail and shifted more toward him. "Now that the tail is good and wet, put it in from behind, then you can enjoy both holes at once."
"You sure about this?" Kai had been using the coils of his tail to hold her in place, but now he took hold of her hips to move her into position while his tail supported her ass.
"Well, maybe make that thing a bit thinner, but trust me, I want this."
After she'd worked him up that much, Kai wasn't going to hold back. He lowered Omilaena onto his cock and grunted as he finally got some relief inside her: the tail fucking had gotten her deliciously wet and ready for him. But then came the new part: he raised the tail and slowly pushed a thinner version of it into her ass.
"Oh, fuck!" Omilaena twitched against him, eyes widening and fingernails digging into his chest. "Feels like you're totally filling me... does it feel good for you too?"
"Yeah, not bad." Kai almost growled his response, hungry for more, but he was actually touched the way she asked. Now that the teasing was over and they were actually having sex, Omilaena truly cared about his pleasure. She might have wanted this, but she also wanted it to be good for him.
Well, it was good: having something in her ass made Omilaena clench up in a way she didn't normally, leaving her pussy tighter around his cock. He could thrust inside her from the front, but even a gentle thrust from behind made her push forward and clench again. In a strange way he felt like he had total control of her hips and her movements, leaving her helpless in his grip.
So he began to fuck her for real. Kai reached down with both hands to get a good feel of her ass even though his tail held her up easily enough. Omilaena bucked and flailed against him, moaning in pleasure as he dominated her movements while thrusting into both holes. She'd started out with her fingernails against his chest and soon she'd wrapped her arms around his neck, holding on for dear life.
Kai chuckled as he began to master the new technique, using it to drive Omilaena to the heights of pleasure. He could change things up, using the coils of his tail to pull her into each thrust of his cock. And after one orgasm when she clung to his chest, he stopped those thrusts, just pounding his tail into her from behind and enjoying how she spasmed with each one.
As soon as he relaxed and stopped thinking about the details of what he was doing, the pleasure was almost enough to overwhelm him. Kai gritted his teeth and held off until she came again, then her pussy was too much: he exploded inside her, releasing jets of his seed until at last she was trembling against him.
For a while she remained there, panting for breath happily... then he saw a mischievous smile reemerge.
"You know... the tail didn't come," Omilaena pointed out.
"You cannot be serious."
"But wouldn't it be beneficial to have a tail that could spit out a liquid? You could probably manage jets of poison, and then you could fill me up in both holes simultaneously."
"Are you really asking me to shoot poison techniques into you?"
"Do it for science!"